Viruses and other selfish genetic elements are dominant entities in the biosphere, with respect to both physical abundance and genetic diversity. Various selfish elements parasitize on all cellular life forms. The relative abundances of different classes of viruses are dramatically different between prokaryotes and eukaryotes. In prokaryotes, the great majority of viruses possess double-stranded (ds) DNA genomes, with a substantial minority of single-stranded (ss) DNA viruses and only limited presence of RNA viruses. In contrast, in eukaryotes, RNA viruses account for the majority of the virome diversity although ssDNA and dsDNA viruses are common as well. Phylogenomic analysis yields tangible clues for the origins of major classes of eukaryotic viruses and in particular their likely roots in prokaryotes. Specifically, the ancestral genome of positive-strand RNA viruses of eukaryotes might have been assembled de novo from genes derived from prokaryotic retroelements and bacteria although a primordial origin of this class of viruses cannot be ruled out. Different groups of double-stranded RNA viruses derive either from dsRNA bacteriophages or from positive-strand RNA viruses. The eukaryotic ssDNA viruses apparently evolved via a fusion of genes from prokaryotic rolling circle-replicating plasmids and positive-strand RNA viruses. Different families of eukaryotic dsDNA viruses appear to have originated from specific groups of bacteriophages on at least two independent occasions. Polintons, the largest known eukaryotic transposons, predicted to also form virus particles, most likely, were the evolutionary intermediates between bacterial tectiviruses and several groups of eukaryotic dsDNA viruses including the proposed order “Megavirales” that unites diverse families of large and giant viruses. Strikingly, evolution of all classes of eukaryotic viruses appears to have involved fusion between structural and replicative gene modules derived from different sources along with additional acquisitions of diverse genes.

Graphic by Ed Rybicki

Ed Rybicki's insight:

Wow...! A tour de force. Quite simply, says it all. REALLY nice piece of work!! And of course, they back me up in my view of how ss(-)RNA viruses evolved. Again B-)

Although arthropods are important viral vectors, the biodiversity of arthropod viruses, as well as the role that arthropods have played in viral origins and evolution, is unclear. Through RNA sequencing of 70 arthropod species we discovered 112 novel viruses that appear to be ancestral to much of the documented genetic diversity of negative-sense RNA viruses, a number of which are also present as endogenous genomic copies. With this greatly enriched diversity we revealed that arthropods contain viruses that fall basal to major virus groups, including the vertebrate-specific arenaviruses, filoviruses, hantaviruses, influenza viruses, lyssaviruses, and paramyxoviruses. We similarly documented a remarkable diversity of genome structures in arthropod viruses, including a putative circular form, that sheds new light on the evolution of genome organization. Hence, arthropods are a major reservoir of viral genetic diversity and have likely been central to viral evolution.

"other ssRNA viruses – such as the negative sense mononegaviruses, Order Mononegavirales, which group includes Ebola, measles and mumps and rabies viruses – may be evolutionarily much younger. In this latter case, the viruses all have the same basic genome with genes in the same order and helical nucleocapsids within differently-shaped enveloped particles. Their host ranges also indicate that they originated in insects: the ones with more than one phylum of host either infect vertebrates and insects or plants and insects, while some infect insects only, or only vertebrates – indicating a possible evolutionary origin in insects, and a subsequent evolutionary divergence in them and in their feeding targets."

"other ssRNA viruses – such as the negative sense mononegaviruses, Order Mononegavirales, which group includes Ebola, measles and mumps and rabies viruses – may be evolutionarily much younger. In this latter case, the viruses all have the same basic genome with genes in the same order and helical nucleocapsids within differently-shaped enveloped particles. Their host ranges also indicate that they originated in insects: the ones with more than one phylum of host either infect vertebrates and insects or plants and insects, while some infect insects only, or only vertebrates – indicating a possible evolutionary origin in insects, and a subsequent evolutionary divergence in them and in their feeding targets."

Interestingly, a virus was discovered in the the horsefly pool that showed sequence homology to tenuiviruses (like rice grass stunt virus) despite the fact that this virus lacked the ambisense coding strategy of teniuviruses. It was discussed that it possibly represents an intermediary form between plant infecting and arthropod-specific viruses.

We present a proof-of-concept three-dimensional reconstruction of the giant mimivirus particle from experimentally measured diffraction patterns from an x-ray free-electron laser. Three-dimensional imaging requires the assembly of many two-dimensional patterns into an internally consistent Fourier volume. Since each particle is randomly oriented when exposed to the x-ray pulse, relative orientations have to be retrieved from the diffraction data alone. We achieve this with a modified version of the expand, maximize and compress algorithm and validate our result using new methods.

West Africa's Ebola outbreak could be stanched by mid-year – but in the epidemic's wake, another public health crisis looms. Disruption of the region's already feeble health care systems has derailed health campaigns targeting childhood diseases, leaving the door wide open for measles and other preventable illnesses.

President Yahyah Jammeh, the dictator who has defied medical opinion since 2007 by claiming to have found a cure for HIV-AIDS, has found allies in a British homoeopathic group sponsored by the official suppliers of homoeopathic medicine to the Royal...

The world can beat the liver-attacking hepatitis B virus, which results in some 650.000 deaths a year, the World Health Organization said Thursday, releasing its first treatment guidelines for the disease.

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